Resize iframe to actual size of contained window, uses postMessage
Safer to use id selector than impact all iframes on page.

Re pmario comments

Conflicts:
	src/apps/backstage.js.js
Use height of html element not document

html element height = height of content
doc height = height of iframe if set
Merge pull request #1030 from colmjude/resizebs

Resize iframe to actual size of contained window, uses postMessage